1. Field of the Invention
This invention relates to an image display device for an image display by projecting the image on a screen.
2. Description of the Related Art
There have hitherto been known a variety of image display devices, which may roughly be divided into a direct viewing type image display device, such as a cathode ray tube (CRT) or a liquid crystal display (LCD), in which an image displayed on a display surface is viewed, and a projection type image display device, that is an image projecting device or a projection type image display device, in which an image displayed on a projection tube (CRT) or a liquid crystal display device is projected on a screen via an optical system such as a projection lens or a reflecting mirror. The projection type image display device is sub-divided into a rear projector, that is back surface projection type in which an image is projected from the back side of a transmitting screen, and a front projector, that is a front surface projection type in which an image is projected from the front side of a reflective screen.
In keeping up with the diversification in the image industry and developments in image media in information communication in recent years, the need for a high definition, large screen display is rapidly increasing. That is, there is an increasing demand for large sized screen display for household use, as well as a large size screen display for public indoor or outdoor use.
Among the direct viewing picture display devices, the picture display device employing a sole CRT, for example, does not lend itself to an increase in size because of constraints as to the strength, weight and depth. Although it is known to provide a large display surface by arranging direct-viewing small-sized CRTs in X and Y directions in a matrix configuration, the picture obtained in this manner is objectionable because of perceptible gaps between the CRTS.
As for the direct viewing picture display devices, it may be contemplated to provide a large display screen using a sole liquid crystal device. However, a large-size liquid crystal device suffers from increased equipment requirements and poor yield. Although a direct viewing large size screen may be realized by arranging a plurality of small-sized liquid crystal devices or liquid crystal units in the X and Y directions in a matrix array in the same manner as described above, the picture obtained in this manner again is objectionable because of so-called shading at a light output unit despite preventative measures, and perceptible junctions between the separate units or devices.
The projection type picture display device lends itself more easily to realization of a large size display screen because the picture is enlarged in size when projected on the screen. However, in the case of the rear projector of the projection type picture display device, the size of the device tends to increase in depth so that a device of reduced thickness cannot be easily realized despite the use of a reflective mirror for reflecting the picture from the projecting tube or the liquid crystal display device in an effort to reduce the depth. Although it is known with the rear projector to realize a large size display screen by arranging a plurality of small-size projection unit devices in the X and Y directions in a matrix configuration, lattice-shaped junctions lines are left as in the case of the direct viewing X-Y matrix array described above.
In the case of the front projector, the screen itself may be reduced in thickness so that it can be hung on the wall. However, the device suffers from insufficient picture lightness such that it cannot be employed except in a dark room or a poorly lighted chamber.
There is also known a collective type picture display device in which a large number of light emitting display elements are arrayed two-dimensionally in association with pixels of a picture for enlarging the screen size. With this device, it is not possible to reduce the pitch of the pixels without considerable difficulties.
With a so-called plasma display, it is not possible to realize a large size screen simultaneously with high brightness and prolonged service life.
Thus, up to now there remains a need for a picture display device which provides a high quality picture display with an ultra thin and large display surface.